1. Field of the Invention
This invention relates to electric motors and in particular, to a rotor and commutator for use in a fuel pump motor. Fuel pump motors are used in vehicles to transfer fuel from the fuel tank to the engine.
2. Background Art
In a fuel pump motor the fuel passes through the motor allowing the motor and pump to be submerged within the fuel tank or formed as part of the fuel line reducing the risk of leaks between the pump and the motor. The motor is a direct current motor which has a permanent magnet stator and a wound rotor or armature. Brushes and a commutator connect the windings of the rotor to an external power supply. Because the rotor is submerged in fuel, care is taken to make the rotor aerodynamic to reduce the power required to physically turn the rotor within the fuel, which is considerably more than the power required to turn the rotor in air as the fuel is more dense. The difference in power required to turn the rotor between wet and dry running is known as punch losses.
To reduce punch losses, it is known to fully encapsulate the rotor by over molding the rotor, once it has been wound. This is the best solution from a fluid dynamics view point, but the material of the encapsulation also thermally insulates the rotor windings leading to higher winding temperatures and a higher risk of failure. This can be overcome by using larger diameter wire, but this leads to a larger motor and greater cost. The cost of over molding the rotor is also an important disadvantage and there is a problem with segment contamination.
Another known method which is very cost effective is a compromise in which a cover is placed over the end of the rotor remote from the commutator and covers the ends or heads of the windings protruding from this end of the rotor core. This end is the leading end in the fuel flow direction and this cover reduces turbulence at the leading end of the rotor. It also allows some fuel to flow through the rotor in contact with the windings to keep the rotor core and windings cool. However, as the commutator connections and the winding heads at the commutator end are exposed, the punch losses are still significant.
Hence, there is a need for a rotor for a fuel pump motor which has reduced punch losses associated with the commutator connections at a reasonable cost.